This came about as an offshoot of my thoughts in the last post about a special piece of equipment for each character. One of the potential consequences of using that little quasi-rule is that a character, or the player of the character, may develop an emotional attachment to an item.
A little history can do that. Suddenly you have a fighter who wants to hang onto a sword because it belonged to his late father and he wants to use it to bring honor to the family, or because it was a token given to him by his childhood sweetheart, or because he found it behind the stables and it was the sword he learned to fight with. Sometimes an attachment might develop to a perfectly normal weapon with a distinctive appearance, or that was gained in a particulary memorable adventure.
Of course, these swords being normal and non-magical, it would be to the fighter's disadvantage to keep them when enchanted weapons are found during an adventure. Role playing urges one thing, and gaming cries out for the opposite: to cast away a trusty weapon or suit of armor because it doesn't have a +1 or +2 attached to it.
Where do legendary weapons come from, anyway? Can a wizard just make one, or do they require something greater to light the spark within them? What if they're born not of wizardly enchantment, but of a hero's bond to them, and the fame of being irrevocably linked with the hero and his deeds?
When a hero performs a truly heroic deed with a prized weapon or armor, and sincerely praises the item's virtue as a major factor in his victory, the item begins to "awaken." When he or she turns down the opportunity to replace the item with an objectively superior or aesthetically more pleasing model, the bond is formed, the weapon's legend begins to grow, and it gains powers beyond a mere piece of steel. Perhaps this process is analogous, more or less, to an ordinary human attaining level 1 in an adventuring class. It is elevated above the level of its ordinary kin.
With each heroic deed, and each refusal of the hero to forsake his trusty armament, it gains renown until it "levels up." It begins its enchanted life with the ability to harm creatures immune to normal weapons, and over time and great deeds, it gains other powers too: bonuses to attack and damage, special virtues against the hero's sworn foes, and so on. The powers gained should always be in harmony with the personality and goals of the wielder. It may even become conscious and able to communicate with its wielder, and because it is a thing born of his own soul, the two are always in perfect agreement - there is never the contest of wills that is so often fought with other intelligent weapons.
If the hero should ever forsake the weapon, either abandoning it or giving it away to one unworthy of it, its spirit slowly diminishes, and its powers wither and die, and it becomes a sad lump of metal or wood once again. The hero must honor his weapon by handing it down to a worthy successor. If he dies before that is done, the weapon burns with the desire to carry on his legacy, and does not lose its powers, even if wielded by an unworthy person - only the scorn of its creator can destroy its spirit. Of course if it has developed sentience, it does all it can to bend its new "master" to its own ends or to find a more worthy bearer.